Ionization gas flow meter with pulse rate servo

ABSTRACT

An injection flow meter is provided with means for triggering an X-ray beam generator to produce a sheet of ions in gas flowing in a pipeline at a rate determined by a voltage controlled oscillator having a period approximately equal to the transit time of a sheet of ions to a detector downstream. A logic network, activated at approximately the time an ion sheet is to be detected in order to lock out spurious detector pulses, continually determines whether the ion sheet arrives before or after the X-ray beam generator is retriggered to so adjust the control voltage that the X-ray beam generator is continually retriggered at substantially the same time ion sheets are being detected. A failure to detect ion sheets will not affect the last established control voltage thereby dividing the flow into a number of precise units of volume even in the absence of detector pulses.

United States Patent [191 Fishman et al. [4 1 Feb. 27, 1973 [54]IONIZATION GAS FLOW METER Primary EqramirterArchie R. Borchelt WITHPULSE RATE SERVO Attorney-Lindenberg, Freilich & Wasserman [75]Inventors: Jack B. Fishman, Pasadena; William E. Mutschler, La Verne,both [57] ABSTRACT of Calif. An injection flow meter is provided withmeans for [73] Assigneez Nucleonics Development Company, triggering anX-ray beam generator to produce a sheet Monrovia, Calm of ions In gasflowing in a pipeline at a rate determined by a voltage controlledoscillator having a [22] Flled: 1970 period approximately equal to thetransit time of a 21 App] 9 ,230 sheet of ions to a detector downstream.A logic network, activated at approximately the time an ion sheet is tobe detected in order to lock out spurious detector g g "73/194 pulses,continually determines whether the ion sheet [581 mid oraaziiiiiaeayzajreamE 194p eefeee ee efeee ehe X-eey eeem ie retriggered to so adjustthe control voltage that the X- [56] References Cited ray beam generatoris continually retriggered at substantially the same time ion sheets arebeing detected. UNITED STATES PATENTS A failure to detect ion sheetswill not affect the last 2 637 208 5/1953 Meuen 250/43 5 FC xestablished control voltage thereby dividing the flow 216401936 6/1953into a number of precise units of volume even in the 3,302,446 2/1967Schmitt et al. ..73/l94 E x absence of detector P 10 Claims, 5 DrawingFigures B SQUARE WAVE VOLTAGE E REP GEM CONTROLLED OSCILLATOR GEN METERPULSE GEN. c- D 25 2e LOGIC DIGITAL COUNTERY E WOR K INTEGRATOR x 29 E27 I PULSER 14 PULSE x F M R 13 I o N 2 f DE TECTOR PATENTEDFEBZIISTSSHEET 1 OF 3 B SQUARE WAVE VOLTAGE -17 E0 REF. GENI CONTROLLEDOSCILLATOR TRIGGER a 16 RATE GATTING PULSE GEN METER PULSE GEN. c. D a ICO NTER LOGIC DIGITAL U NETWORK R INTEGRATOR PULSER 14 PULSE DETECTOR II I I I I I I I I II I I I II IIII II I I IIIII :I] II H *H 1 GAS T FLOWI JI,,I,I,,,,,,UIIIII I III II I 1 11 I 1 I I I II I I C T Y 7 T. Y I ID W P I P P P z p F I 2 1 2 3| 4 5 E 311' L L INVENTORS JACK B. FISHMANBYWILLIAM E. MUTSCHLER AT TORNEYS PATENTEDFEBZYISB 3 7181143 SHEET 2 OF3 FIG. 3

INVENTORS JACK B. FISHMAN WILLIAM E. MU'TSCHLER BY PAIENTED EBZ3,718,043

saw 3 OF 3 54 y 1 28 E L l MONOsTABLEi I I 27 MONOSTABLE MV 5 LF] a 6427 2s RELAXATION OSCILLATOR cu BINARY COUNTER INVENTORS JACK B, FISHMANF I G 5 mYVILLIAM E. MUTSCHLER ATTORNEYS IONIZATION GAS FLOW METER WITHPULSE RATE SERVO BACKGROUND OF THE INVENTION This invention relates to atracer injection flow me-' ter, and particularly to an ionization flowmeter for monitoring flow rates, such as in natural-gas transmissionlines.

Orifice meters commonly used in natural-gas trans mission lines presentvarious problems and difficulties, such as maintaining the orificediameter constant due to an accumulation of dirt particles over a periodof time, and maintaining a constant flow velocity. A flow meterutilizing a gas ionization principle will overcome the problems anddifficulties of an orifice meter, but for volume flow measurements,system utilizing the gas ionization principle which have been developedin the past have been deficient in accuracy.

A flow meter utilizing the gas ionization principle consists of meansfor ionizing the gas flow at a fixed point in a pipeline to create anion cloud. This cloud of ions is detected at a point a fixed distancedownstream. The detection time lapse is then divided into the distancebetween the point of ionization and the point of detection to obtainflow velocity. From the dimensions of the pipeline, the volume flow isalso determined.

For monitoring flow rates on a continual basis, it has been standardpractice to generate a pulse for triggering the ionizing means inresponse to the last ion cloud detected downstream. The rate at whichthese trigger pulses are generated is then proportional to the flowrate. By counting the number of trigger pulses, a continuous indicationof the total volume of gas flow is obtained.

This ionization technique resembles the conventional technique ofinjecting a tracer into the flow stream and detecting its presencedownstream. However, the ionization technique has several majoradvantages. The principal advantage is that no foreign material isinjected into the flow stream. Since the fiowing gas itself is onlymomentarily transformed to produce the tracer, the gas delivered to theuser is in its initial form with no changes. Another advantage is thatthere is no time lag for the tracer to assume the flow rate of the gasand there is no disturbance to the flow of the gas itself or dispersionof the tracer in the gas. Still another advantage is that since theionizing radiation travels at the speed of light, a complete sheet ofions may be created across the pipe almost instantaneously (in a periodof the order of seconds). Temperature, pressure, density and gascomposition have no effect on this ionization technique. Since thedownstream ion detector is passive, it introduces no disturbance to theflow. The detector will respond to the abrupt change in current producedas the ion sheet passes, and is not dependent on the quantity of ions aslongv as a predetermined minimum quantity is present.

Although an ionization meter overcomes the problems of the orificemeter, and does not involve the injection of a foreign material into thefiow stream, accurate measurements of flow rates and total gas flow isnot possible with present ionization meters because turbulence withinthe pipeline may cause the sheet or cloud of ions to flow around theprobe of the detector such that the measuring system will not registerthe passage of a unit of volume. Although this phenomenon will not occurvery frequently, the error thus produced is cumulative so that after aperiod of time the total quantity of gas not registered will besignificant.

Another problem which exists with ionization meters is that foreignmatter in the gas may occasionally strike the detection probe andproduce random noise pulses. Since some of these noise pulses may be ofsufficient 0 amplitude to be registered by the measuring system,

there is a possibility that a customer may be charged for undeliveredunits of gas. While this type of error may be offset by the occasionalfailure to detect the passage of an ion cloud, it is not possible toanticipate that one type of error will always offset the other. In anycase, either type of error may produce a significant error in flow ratemeasurement over a short period of time.

While the preferred embodiment of the present invention is in anionization meter, because of the inherent advantages just pointed out,it should be understood that in its broadest aspects, the presentinvention may be advantageously employed in many known tracer injectionflow meters.

OBJECTS AND SUMMARY OF THE INVENTION An object of the present inventionis to provide a tracer injection meter that will register a unit of gasflow even though there is a failure to detect the passage of an injectedtracer.

Still another object is to provide a tracer injection meter that willnot register noise pulses which may occur between tracer detectionpulses.

Yet another object is to provide a tracer injection meter that willcontinue to register gas flow during a failure to detect tracers basedon the current flow rate at the time of failure.

These and other objects of the invention are achieved in a tracerinjection meter having means at a fixed station for injecting a tracerin a fluid flow stream, and means for detecting the tracers as they flowpast a fixed station downstream from the ionization station. Anoscillator controlled by a voltage signal is employed to drive asquare-wave signal generator which triggers the tracer injection meansat the center of each cycle.

The voltage controlled oscillator is also employed to drive a generatorof gating pulses that are centered about the center of the square-wavesignal, and therefore are centered on the triggering times of the tracerinjections. Means comprising a digital logic network receives the outputsignals of the tracer detecting means, the square-wave signal, and thegating pulses to determine whether a tracer is being detected atapproximately the time the tracer injecting means is being triggered,and to further determine whether the tracer is detected too early or toolate with respect to the triggering of the tracer generating means. Thelogic network means produces an error pulse of a given binarycharacteristic if the tracer is detected late. Pulses of the givencharacteristic are integrated, and the result of integration is combinedwith the reference voltage to decrease the period of the oscillator.Pulses of complementary characteristic produced by the logic networkmeans when the tracers are detected too early are also integrated withthe opposite effect on the control voltage. When there is a momentary ortemporary failure to detect tracers, error pulses are not produced, and

the control voltage is left at the last adjusted level to providecontinued indication of gas flow at the rate established at the time offailure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates schematically apreferred embodiment of the present invention.

FIG. 2 illustrates a timing diagram of signal waveforms appearing atdesignated points in FIG. 1.

FIG. 3 illustrates a circuit employed in the system of FIG. 1 forgenerating the signals of waveforms A, B, C and D, of FIG. 2.

FIG. 4 illustrates a logic network employed in the system of FIG. 1.

FIG. 5 illustrates a circuit employed in the system of FIG. 1 forintegrating error pulses and for continually combining the result ofintegration with a reference voltage.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIG. 1, theionization type of injection meter embodying the present invention isshown monitoring flow rates in a natural gas transmission line 10, butit should be understood that the ionization meter may be employed toequal advantage for monitoring flow rates of any gas in a pipe.

Flowing gas is ionized at a fixed station 11 by a transverse fan-shapedbeam of relatively low-energy electromagnetic radiation. This beamproduces a sheet of ions, and in that way effectively injects a tracerthat is detected at a fixed station 12 a predetermined distance (a fewfeet) downstream. To produce the beam, an X- ray (vacuum diode) tube 13is triggered by a short (1 ms) high voltage pulse through a transformer14 by a pulser 15 in a conventional manner using techniques developed inmedical X-ray equipment.

Each cycle of the pulser 15 is initiated by a pulse from a generator 16driven by an oscillator 17 through a square-wave generator 18. Theoscillator is preferably one which may be directly controlled by avoltage signal E derived directly from a digital integrator 19 to bedescribed with reference to FIG. 5.

An ion detector 24 comprising a probe in the pipe detects each sheet ofions at a station 12 and transmits a pulse through a logic network 25.The logic network receives timing signals from the square-wave generator18 and a gating pulse generator 26 to determine whether a sheet of ionsproduced at the station 11 is being detected at the station 12 early orlate with respect to the time the trigger pulse generator 16 againpulses the X-ray tube 13 through the transformer 14 to produce anothersheet of ions. If it is determined that a sheet of ions has beendetected early, the logic network 25 causes a pulse to be applied to theintegrator 19 via a line 27 to increase the control voltage E applied tothe oscillator 17, and thereby decrease the oscillator period (increasethe oscillator frequency). If it is determined that a sheet of ions isdetected late, an error pulse is applied to the integrator 19 via a line28, thereby decreasing the control voltage E to increase the period(decrease the frequency) of the oscillator Once a sufficient number oferror pulses have been integrated to adjust the period of the oscillator17 to a value substantially equal to the transit time of the gas flowfrom the station 1 1 to station 12, the logic network 25 will continueto make definitive too early and too late determinations. Therefore, theservo control thus provided may hunt back and forth around the periodprecisely equal to the transit time between the stations 11 and 12, butonly while the ion detector 24 is transmitting pulses to the logicnetwork 25. To minimize this hunting effect, the change in the controlvoltage E produced by each pulse is selected to be suf ficiently smallto maintain the period of the oscillator substantially stable.

If turbulence exists within the pipeline 10, and the ion detector 24fails to detect the passage of an ion sheet, the logic network 25 willnot transmit an error pulse on either line 27 or line 28, therebyleaving the control voltage E unaltered. The oscillator 17 will thencontinue to operate at the last adjusted frequency to time thegeneration of subsequent sheets of ions. A counter 29 accumulates thetrigger pulses from the generator 16 to provide an accurate measure ofthe quantity of gas transmitted through the pipeline. If the X-ray tube13 were not pulsed at approximately the time an ion sheet is beingdetected, because the detector misses the passage of an ion sheet, therewould be a failure to record accurately the last unit of gas transmittedpast the station 11. If several successive ion sheets are not detectedbecause of a momentary or temporary failure to ionize sheets of gas, orto detect ionized sheets, the oscillator 17 will continue to drive thetrigger pulse generator 16 to supply pulses to the counter 29 at asteady rate based on the X-ray trigger rate established at the time offailure.

If foreign matter present in the gas should strike the probe of the iondetector 24 in such a manner as to produce random noise pulses ofsufficient amplitude to cause the logic network 25 to perform itsfunction, they will be rejected by the logic network 25 unless theyoccur within the period of a pulse from the generator 26 centered aboutthat point in the period of the output from the oscillator 17 at whichthe X-ray tube 13 is pulsed. If such a noise pulse should occur duringthe period of a pulse from the generator 26, either before or after theion sheet is actually detected, a spurious too early error pulse may beapplied to the integrator 19 via line 27 thereby erroneously alteringthe frequency of the oscillator 17. However, the counter 29 responds toonly the pulse transmitted by the trigger pulse generator 16, and theeffect of erroneously adjusting the frequency of the oscillator 17 willbe quickly correctedby the logic network during the next cycle of theoscillator 17.

Operation of the illustrated embodiment of the present invention maybest be understood from waveforms A to E of FIG. 2 which appear atpoints indicated by corresponding reference letters in FIG. 1. Eachcycle of the waveform A produced by the oscillator I9 drives thesquare-wave generator 18 to produce the waveform B. The trigger pulsegenerator 16 differentiates the square waveform B to produce thenegative going trigger pulses of the waveform C. Each trigger pulseactuates the pulser 15 to trigger the X-ray tube 13 through thetransformer 14. The trigger pulses are also applied to the counter 27,as noted hereinbefore.

The waveform A also drives the gating pulse generator 26 to produce thewaveform D applied together with the waveform B to the logic network 25.Each ion sheet produced at station 11 by a trigger pulse of waveform Cis detected at the station 12 by the ion detector 24 which transmits apulse to the logic network 25 as shown by the waveform E. The first iondetector pulse l occurs before the X-ray trigger pulse of the firstcycle of the oscillator 17 shown. The logic network 25 determines thatthe pulse l has occurred too early by noting that it has occurred whileonly the waveform D of the waveforms B and D is positive. Accordingly,the logic network 25 produces a pulse of fixed duration to drive theintegrator 19. The result is an increase in the control voltage E todecrease the period of the oscillator 17.

It is assumed that the correction introduced by the error pulsesproduced on line 27 is not sufficient to completely adjust the period ofoscillator 17 after the first return pulse P from the ion detector 24.Then the second return pulse P also occurs too early and producesanother error pulse on the line 27 to further decrease the period of theoscillator 17.

It should be noted that comparison is made between the leading edge ofeach return pulse of the waveform C and a positive going edge of thewaveform B, but that comparison is restricted to a fraction of theperiod of the waveform B by the waveform D. it should further be notedthat the relative amplitudes and periods of the waveforms shown havebeen selected for purposes of explanation only. in practice, the periodsof the gating pulses of the waveform D are selected to be percent of theperiod of the waveform A.

Assuming that the second error pulse adjusts the period of theoscillator 17 to precisely the transit time of a sheet of ions, thethird return pulse P will occur precisely at the center of the nextcycle of the oscillator 17. In that event there is ambiguity as towhether an ion detector pulse P has occurred early (while only thewaveform B is positive) or late (when both the waveforms B and D arepositive). Under those conditions, it would be ideal for either both orneither a too early nor a too late error pulse to be produced. The netvoltage change applied to the integrator 19 would then be zero and theperiod of the oscillator 17 would remain unchanged. However, it is moreconvenient to design the logic network to resolve the ambiguity bydetermining that it has occurred early. Each too early error pulseproduced inhibits that part of the logic network employed to determinewhen the return pulse has occurred too late.

if the velocity of the gas flowing through the line 10 remainsunchanged, the next return pulse P, will occur too early and an errorpulse will be produced on the line 27. The next return pulse 1, willthen occur too late, thereby causing an error pulse to be produced online 28. Thereafter, the logic network 2 may continue to cause errorpulses to be produced alternately on lines 27 and 23 as long as thevelocity of the gas does not change. Thus, as noted hereinbefore, theservo control provided may cause the period of the oscillator 17 tohunt, but if the correction introduced by each error pulse is verysmall, the resulting changes in the period of the oscillator 17 will bevery small. In any event, the average period of the oscillator 17 willbe correct and the quantity of gas registered by the counter 29 will beaccurate. Moreover, the degree of accuracy achieved will not depend uponthe gas flow rate.

A rate meter 30 is connected to receive trigger pulses from thegenerator 16 and display the current flow rate in appropriate units. Forexample, each trigger pulse may be applied to monostable multivibratorof fixed period. The output of the multivibrator may then gate pulses ofconstant height and width at a fixed rate to an RC integrator. Thedesired scaling is then selected by setting the rate of the pulsesapplied to the integrator. Scaling may also be achieved by varying theresistance of the discharge path of the integrating capacitor whileholding the rate of the gated pulses constant.

Referring now to FIG. 3, a circuit for generating the waveforms A, B, Cand D of FIG. 2 will now be described. The oscillator for generating thesawtooth waveform A comprises an integrator consisting of an operationalamplifier 31 and a feedback capacitor 32 connected by a resistor 33 toreceive from the digital integrator 19 (FIG. 1) the control voltage E ofpositive and negative polarities through field-effect transistors Q and0 An operational amplifier 34 having a negative feedback resistor 35receives the positive control voltage (+E through a resistor 36 anddelivers to the drain of the transistor Q the negative control voltage(-E Assuming that the positive control voltage is +5 volts, and that thetransistor Q has been conducting for some time, the output of theamplifier 31 will be at 5 volts, the starting point for a cycle of thewaveform A in FIG. 2.

A comparator comprising a high gain differential amplifier 37 having afeedback resistor 38 to the positive input terminal compares the outputof the amplifier 31 with a fixed reference provided by a voltagedividing network consisting of resistors 39 and 40. Assuming the fixedreference is slightly less than 5 volts, such as 4.95 volts, whennegative going the output of the amplifier 31 becomes more negative thanthat reference, the output of the comparator switches from a level ofabout +4.95 volts to a level of about -4.95 volts. The negative outputof the comparator then reverse biases a diode D to turn a transistoroff, thereby turning the field-effect transistor Q off and, through atransistor Q turning the field-effect transistor Q on. Once thetransistor Q turns on, the output of the amplifier 31 will increase from-5 volts to about 1 volt to produce the first half of the first cycle inthe waveform A.

When the output of the amplifier 31 reaches'the 1 volt level, the outputof the amplifier 37 will switch from -5 volts to +5 volts to againforward bias the diode D turn the transistor 0,, on and thereby turn thetransistor Q off while turning the transistor Q on. That restores thepositive control voltage (+E to the amplifier 31 so that its output willbe driven at a constant rate from about 1 volt toward -5 volts tocomplete the first cycle of the waveform A. The rate at which the outputof the amplifier 31 is driven from 5 volts to 1 volt and thereafter backto 5 volts is dependent upon the amplitude of the control voltage E Thegreater the control voltage amplitude, the greater the rate, andtherefore the higher the frequency of the oscillator.

The output of the amplifier 37 is applied directly to the logic network25 (FIG. 1) as a square wave of the same frequency as the sawtoothwaveform, as shown by the waveform B of FIG. 2.

The waveform B is differentiated by a capacitor 41 and resistor 42 toprovide negative and positive spikes at negative and positive goingedges. The positive spikes are inverted by a transistor while thenegative spikes are suppressed due to reverse biasing of thebase-emitter junction of the NPN transistor Q thereby producing thewaveform C.

The sawtooth waveform A at the output of the amplifier 31 is applied tothe negative (inverting) terminal of a high gain differential amplifier43 through a. resistor 44 while a reference voltage V, is applied to thepositive (noninverting) terminal from a voltage dividing networkcomprising resistors 45 and 46. The resistor 46 may be a potentiometeras shown to adjust the voltage -V,. to any desired level. The voltageV,. (represented in FIG. 2 by a horizontal dotted line in the waveformA) is set at a median level of the waveform A so that the output of theamplifier 43 is a train of negative pulses, each at the center of thecurrent cycle of the waveform A and of a period equal to 50 percent ofthe period of waveform A cycle. The negative pulses thus produced areinverted by a transistor Q, to produce the waveform D.

It should be noted that the period of each pulse in the waveform D hasbeen shown as 50 percent of the corresponding cycles of the waveform Afor simplicity of explanation only. In practice, the period of eachpulse would be set to about percent, as noted hereinbefore, by adjustingthe reference voltage V, until each pulses of the waveform D is onlyapproximately 10 percent of the current cycle of the waveform A.

Referring now to FIG. 4, the logic network 25 which receives thewaveforms B and D, and the ion detector pulses shown in the waveform E,will now be described. NAND gates 51 and 52 functioning as AND gatesreceive the waveform D directly while the NAND gate 52 receives thewaveform B through an inverter 53.

The return pulses from the ion detector are applied to the NAND gates 51and 52 to trigger one of two monostable multivibrators 54 and 55depending upon whether a given return pulse has been received too late,in which case, it is transmitted only through the NAND gate 51, or tooearly, in which case it is transmitted only through the NAND gate 52.Both output terminals of the NAND gates 51 and 52 are connected to NANDgate 56 functioning as an OR gate to turn on a transistor 0 and energizean incandescent lamp 57 each time an ion detector pulse is beingreceived within the periods of the gating pulses shown in the waveform Dof FIG. 2.

The gates 51 and 52 are implemented as NAND gates so that cy connectingthe output of the NAND gate 52 directly to a NAND gate 58, and theoutput of the NAND gate 51 to the NAND gate 58 through an inverter 59, areturn pulse transmitted by the NAND gate 52 will be inverted toeffectively lock out a return pulse transmitted by the NAND gate 51.Accordingly, if a sheet of ions is detected at precisely the time theX-ray tube 13 is being triggered by a pulse in the waveform C, a returnpulse may cause'both NAND gates 51 and 52 to transmit a pulse, but onlythe output of the NAND gate 52 is transmitted to the monostablemultivibrator 55 via NAND gates 60 and 61. The output of the NAND gate51 will not trigger the monostable multivibrator 54 via NAND gates 62and 63 while the AND gate 52 is transmitting an ion detector pulse.

This lockout arrangement, which gives preference to a too early"indication in the event of ambiguity due to an ion trigger pulse beingdetected at precisely the center of a cycle of the waveform A, iseffective for only narrow return pulses. Wide return pulses couldproduce output signals through the NAND gate 51 to trigger themonostable multivibrator 54 after the NAND gate 52 is no longertransmitting an output signal. Accordingly, it is preferred that thereturn pulses from the ion detector 24 (FIG. 1) be short, highpeakpulses.

The output pulses from the monostable multivibrators 54 and aretransmitted to the integrator 19 (FIG. 1) via lines 27 and 28. However,if the integrator is responsive to only the leading edges of the pulsesfrom the monostable multivibrators, failure to lock out the output ofthe NAND gate 51 would simply result in a too late" indicationcancelling the too early indication, thereby leaving the control voltageE unaltered. Except for a negligible period of time, the change in theperiod waveform A during the next cycle would not be noticeable. This,of course, assumes the response time of the integrator 19 issufficiently short to respond to the leading edges of both too early andtoo late pulses. If not the integrator will inherently lock out the toolate" pulse.

The NAND gates to 63 are provided to enable the integrator 19 to be runup or down manually for initial acquisition of ion detector pulseswithin the periods of pulses in the waveform D. A double pole, threeposition switch S, connects circuit ground to the NAND gates 60 and 62to lock out pulses from the AND gates 51 and 52 during manualacquisition. The second pole of the switch 60 connects a free runningrelaxation oscillator 64 to either the NAND gate 61 or the NAND gate 63,depending upon whether the integrator 19 is to be run up or down foracquisition.

The digital integrator will now be described with reference to FIG. 5.It consists of an updown binary counter 65 with preset input terminalsconnected to circuit ground so that when a reset switch S is momentarilyclosed, the counter is set to a predetermined number, such as 25, whichis empirically found to correspond to a flow rate below the expectedrange of flow rates, typically 5 to 40 feet per second. Once the counterhas been reset to the predetermined number, the manual acquisitionswitch S, (FIG. 4) is operated to cause the counter to count up untilreturn pulses are being received from the ion detector during theperiods of the pulses in the waveform D, at which time the lamp 57 willbe triggered on by the acquired ion detector pulses. Thus, by alwaysstarting from a count known to be low low, instead of from a median,apparatus (such as an oscilloscope) is not required to determine thedirection the integrator should be run for manual acquisition. As analternative to manual acquisition, an automatic acquisition circuit maybe included, again starting from a count known to be too low tofacilitate implementation.

Once return pulse acquisition has been achieved, the switch S, isreturned to its neutral position to allow the logic network 25 andintegrator 19 to continually drive the period of the waveform A towardthe period of the detected pulses. That is accomplished by varying thecontrol voltage E in accordance with the digital output of the counter65. The range of the control voltage is preferably from +30 millivoltsto +8 volts with a median of +4 volts. That median is set by apotentiometer 66 connected to a source of fixed negative voltage (about6 volts) provided by a zener diode D connected to a source of l2 voltsthrough a resistor 67. An operational amplifier 68 having a negativefeedback resistor 69 equal to a coupling resistor 70 inverts thenegative voltage selected through the potentiometer 66 to provide apositive median control voltage to the positive input terminal of a highgain differential amplifier 71 having a negative feedback resistor 72connected to its inverting input terminal.

The positive control voltage from the amplifier 68 is coupled to thenegative input terminal of the amplifier 71 through a resistor 73 equalto the negative feedback resistor 72 via a differential amplifier 74connected as a non-inverting operational amplifier. With the outputvoltages from the amplifiers 68 and 74 of equal amplitude and the samepolarity, the output voltage E, from the amplifier 71 is zero. For themedian control voltage E of approximately +4 volts desired when thecounter 65 is counted up to a median number, digitalto-analog convertingresistors R through R are connected to the summing junction between theresistors 72 and 7 3.

The resistors R, to R are weighted for converting a binary number intoan analog voltage. Therefore, each successive one of the resistor R,through R is half the value of its preceeding resistor, and the resistorR for the least significant bit is so selected that with thepredetermined number set in the counter 65, the output of the amplifier71 is at the desired level of approximately 30 millivolts.

Although a straight binary counter is shown for simplicity, in practiceit may be desirable to employ a binary-coded decimal counter. Theconverting resistors would then be binary coded in groups of four, witheach successive group of four weighted ten times as much.

The respective digital-to-analog converting resistors R through R areconnected to output terminals 2 to 2, respectively, of the binarycounter 65. When a given output terminal 2" of the counter 65 is true,the switch connected thereto is turned on to connect the associatedconverting resistor R,,+l to circuit ground. For example, when the mostsignificant bit of the counter 65 is true, a switching transistor Q11 isturned on to connect the resistor R to ground. While the transistor O isnot turned on, the resistor R is efi'ectively removed from the circuitthat determines the voltage at the negative input terminal of theamplifier 71, and therefore out of the circuit that determines the levelof the control voltage E transmitted to the voltage controlledoscillator 17 (FIG. 1).

Although a particular embodiment of the invention has been described andillustrated herein, it is recognized that modifications and variationsmay readily occur to those skilled in the art, such as injecting othertypes of tracers, particularly for monitoring the flow of a liquidinstead of a gas since ions will recombine too quickly in liquids. Forexample, radioactive isotopes of the liquid may be effectively injectedusing a particle emitter such as gamma ray gun in place of the X-ray gundisclosed for effectively injecting ions as tracers.

iii

The radioactive isotopes will then emit various radiations, each havinga certain half-life. A radiation detector may then be employed at thetracer detecting station. Accordingly, it is intended that thelimitation of injecting a tracer into a fluid cover both the effectiveinjection of ions as well as the actual injection of tracers of otherforms and: that the claims be so interpreted as well as to cover othermodifications and variations which may readily occur to those skilled inthe art.

What is claimed is: 1. Apparatus for monitoring the flow of fluid in apipeline comprising controlled means for periodically generating triggerpulses, means responsive to said trigger pulses for injection into saidfluid at a first fixed station in said pipeline tracers which may becarried by said fluid, one

tracer for each trigger pulse,

means at a second fixed station downstream from said first fixed stationfor detecting said tracers,

means responsive to said tracer detecting means for controlling saidtrigger pulse generating means to generate trigger pulses substantiallyin time coincidence with the anticipated detection of tracers based uponthe rate at which tracers have been detected most recently, and

means responsive to said trigger pulses for continually producing atleast one of two types of flow measurements, said types being cumulativevolume and flow rate.

2. A flow meter for monitoring the flow of fluid in a pipelinecomprising controlled means for periodically generating trigger pulses,

means responsive to said trigger pulses for injecting into said fluid ata first fixed station in said pipeline tracers which may be carried bysaid fluid, one tracer for each trigger pulse,

means at a second fixed station downstream from said first fixed stationfor detecting said tracers and for producing a return pulse in responseto each tracer detected,

error detecting means for determining whether a return pulse is producedby said tracer detecting means early or late with respect to triggerpulses generated by said controlled means,

control means responsive to said error detecting means for controllingsaid trigger pulse generating means to generate trigger pulses atsubstantially the same times that tracers are being detected by saidtracer detecting means, and

means responsive to said trigger pulses for continually producing atleast one of two types of flow measurements, said types being cumulativevolume and flow rate.

3. A flow rate meter as defined in claim 2 wherein said trigger pulsegenerating means is controlled by an electrical signal to generatetrigger pulses at a rate proportional to the amplitude of said signal,and said control means comprises means for generating an early or a lateerror pulse according to whether said error detecting means determineswhether a given pulse produced by said tracer detecting means occurredtoo early or too late with respect to a trigger pulse for injecting thenext tracer to be detected,

means for integrating said early and late error pulses,

and

means responsive to said integrating means for altering the amplitude ofsaid control signal in response to each error pulse in a direction whichwill cause the next pulse generated by said tracer detecting means to bedetected closer in time to a trigger pulse generated to inject the nexttracer to be generated.

4. A flow rate meter as defined in claim 3 wherein said integratingmeans comprises digital means for counting in one direction in responseto an early error pulses and in an opposite direction in response to alate error pulse, whereby a high degree of stability in the controlsignal is achieved for extended periods during which tracers are notdetected.

5. A flow rate meter as defined in claim 3 wherein said means forgenerating said pulses includes means for generating a square-wave andmeans for timing said trigger pulses to occur at the center of eachcycle of said square-wave, and wherein said error detecting meansincludes means for comparing the time of a de tector pulse with thephase of said squarewave to determine whether a tracer has been detectedtoo early or too late.

6. A flow rate meter as defined in claim 5 wherein said controlled meansfor generating said trigger pulses further includes means for generatinggating pulses, each gating pulse of a duration that is a predeterminedfraction of the current cycle of said periodic trigger pulse generatingmeans and centered on the time that a trigger pulse is generated at thecenter of said current cycle, and said comparing means is responsive tosaid gating pulse generating means to enable an error determination tobe made only during the presence of a gat ing pulse.

7. A flow rate meter as defined in claim 6 wherein said controlled meansfor generating said trigger pulses comprises means for generating asymmetrical sawtooth waveform of substantially constant amplitude with aperiod directly proportional to the amplitude of said control signal,and

said gating pulse generating means comprises means responsive to saidsawtooth waveform for producing said gating pulses when said sawtoothwaveform exceeds a predetermined level, whereby the period of eachgating pulse is a substantially constant percentage of the cycle of saidsawtooth waveform during which generated, and each gating pulse iscentered about the center of the cycle of said sawtooth waveform duringwhich generated.

8. A flow rate meter as defined in claim 7 wherein said controlled meansfor periodically generating trigger pulses comprises means responsive tosaid sawtooth waveform for producing a trigger pulse at said center ofeach cycle of said sawtooth waveform.

9. A flow rate meter as defined in claim 8 wherein said means responsiveto said sawtooth waveform for producing a trigger pulse at said centerof each cycle of said sawtooth waveform comprises means responsive tosaid sawtooth waveform for generating a square waveform, each cyclehavinga period of said period corresponding directly to the sawtoothwaveform means for differentiating said square waveform to produce sharppulses of a given polarity at the beginning of each cycle of said squarewaveform and of an opposite polarity at the center of each waveform, and

means for suppressing said sharp pulses of said given polarity.

10. A flow rate meter as defined in claim 9 wherein said error detectingmeans comprises two three-terminal gates, each connected to receive saidreturn pulses and said gating pulses at two terminals, and one of saidgates connected to receive said square waveform, and

an inverter coupling said square waveform to the other one of said twogates.

i l l III

1. Apparatus for monitoring the flow of fluid in a pipeline comprisingcontrolled means for periodically generating trigger pulses, meansresponsive to said trigger pulses for injection into said fluid at afirst fixed station in said pipeline tracers which may be carried bysaid fluid, one tracer for each trigger pulse, means at a second fixedstation downstream from said first fixed station for detecting saidtracers, means responsive to said tracer detecting means for controllingsaid trigger pulse generating means to generate trigger pulsessubstantially in time coincidence with the anticipated detection oftracers based upon the rate at which tracers have been detected mostrecently, and means responsive to said trigger pulses for continuallyproducing at least one of two types of flow measurements, said typesbeing cumulative volume and flow rate.
 2. A flow meter for monitoringthe flow of fluid in a pipeline comprising controlled means forperiodically generating trigger pulses, means responsive to said triggerpulses for injecting into said fluid at a first fixed station in saidpipeline tracers which may be carried by said fluid, one tracer for eachtrigger pulse, means at a second fixed station downstream from saidfirst fixed station for detecting said tracers and for producing areturn pulse in response to each tracer detected, error detecting meansfor determining whether a return pulse is produced by said tracerdetecting means early or late with respect to trigger pulses generatedby said controlled means, control means responsive to said errordetecting means for controlling said trigger pulse generating means togenerate trigger pulses at substantially the same times that tracers arebeing detected by said tracer detecting means, and means responsive tosaid trigger pulses for continually producing at least one of two typesof flow measurements, said types being cumulative volume and flow rate.3. A flow rate meter as defined in claim 2 wherein said trigger pulsegenerating means is controlled by an electrical signal to generatetrigger pulses at a rate proportional to the amplitude of said signal,and said control means comprises means for generating an early or a lateerror pulse according to whether said error detecting means determineswhether a given pulse produced by said tracer detecting means occurredtoo early or too late with respect to a trigger pulse for injecting thenext tracer to be detected, means for integrating said early and lateerror pulses, and means responsive to said integrating means foraltering the amplitude of said control signal in response to each errorpulse in a direction which will cause the next pulse generated by saidtracer detecting means to be detected closer in time to a trigger pulsegenerated to inject the next tracer to be generated.
 4. A flow ratemeter as defined in claim 3 wherein said integrating means comprisesdigital means for counting in one direction in response to an earlyerror pulses and in an opposite direction in response to a late errorpulse, whereby a high degree of stability in the control signal isachieved for extended periods during which tracers are not detected. 5.A flow rate meter as defined in claim 3 wherein said means forgenerating said pulses includes means for generating a square-wave andmeans for timing said trigger pulses to occur at the center of eachcycle of said square-wave, and wherein said error detecting meansincludes means for comparing the time of a detector pulse with the phaseof said squarewave to determine whether a tracer has been detected tooearly or too late.
 6. A flow rate meter as defined in claim 5 whereinsaid controlled means for generating said trigger pulses furtherincludes means for generating gating pulses, each gating pulse of aduration that is a predetermined fraction of the current cycle of saidperiodic trigger pulse generating means and centered on the time that atrigger pulse is generated at the center of said current cycle, and saidcomparing means is responsive to said gating pulse generating means toenable an error determination to be made only during the presence of agating pulse.
 7. A flow rate meter as defined in claim 6 wherein saidcontrolled means for generating said trigger pulses comprises means forgenerating a symmetrical sawtooth waveform of substantially constantamplitude with a period directly proportional to the amplitude of saidcontrol signal, and said gating pulse generating means comprises meansresponsive to said sawtooth waveform for producing said gating pulseswhen said sawtooth waveform exceeds a predetermined level, whereby theperiod of each gating pulse is a substantially constant percentage ofthe cycle of said sawtooth waveform during which generated, and eachgating pulse is centered about the center of the cycle of said sawtoothwaveform during which generated.
 8. A flow rate meter as defined inclaim 7 wherein said controlled means for periodically generatingtrigger pulses comprises means responsive to said sawtooth waveform forproducing a trigger pulse at said center of each cycle of said sawtoothwaveform.
 9. A flow rate meter as defined in claim 8 wherein said meansresponsive to said sawtooth waveform for producing a trigger pulse atsaid center of each cycle of said sawtooth waveform comprises meansresponsive to said sawtooth waveform for generating a square waveform,each cycle having a period corresponding directly to the period of saidsawtooth waveform, means for differentiating said square waveform toproduce sharp pulses of a given polarity at the beginning of each cycleof said square waveform and of an opposite polarity at the center ofeach waveform, and means for suppressing said sharp pulses of said givenpolarity.
 10. A flow rate meter as defined in claim 9 wherein said errordetecting means comprises two three-terminal gates, each connected toreceive said return pulses and said gating pulses at two terminals, andone of said gates connected to receive said square waveform, and aninverter coupling said square waveform to the other one of said twogates.